Hi @Bradley Cartledge ,
Sorry for delay.
According to my tests in Outlook 2016 and Outlook 2019, the building blocks is stored in NormalEmail.dotm, I also haven't found the option to change it. However, I found we could try to copy the NormalEmail.dotm file directly to deploy the Quick Part, if you haven't tried it. As a suggestion, it's recommended to copy and paste this file to same location to check.
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